Global patterns in water flux partitioning: Irrigated and rainfed agriculture drives asymmetrical flux to vegetation over runoff

The partitioning of precipitation water input on land between green (evapotranspiration) and blue (runoff) water fluxes distributes the annually renewable freshwater resource among sectors and ecosystems. The patterns and main drivers of this partitioning are not fully understood around the global land area. We decipher the worldwide patterns and key determinants of this water flux partitioning and investigate its predictability based on a global machine learning model. Available data for 3,614 hydrological catchments and model application to the global land area agree in showing mostly larger green than blue water flux. Possible expansion/intensification of irrigated and/or rainfed agriculture to feed a growing human population, along with climate warming, will tend to increase this flux partitioning asymmetry, jeopardizing blue water security. The developed machine learning model presents a promising predictive tool for future blue and green water availability under various forthcoming climate and land-use change scenarios around the world. [Display omitted] •Machine learning model developed for green-blue water flux partitioning around the world•Flux partitioning to crops and other vegetation is mostly higher than to runoff•Agricultural expansion/intensification under warming decreases blue water security As the main source of freshwater on land, precipitation filters into the soil where some of it is used by plants as a “green water flux” and some flows into rivers as the visible “blue water flux.” How much water ends up in the “green” flux is key for sustaining crops and other vegetation, and for societal food security. The “blue” water flux sustains the aquatic ecosystems, and is also critical for societal water security, e.g., for drinking water but also for crop irrigation, which shifts blue water into green. Our study shows that the green flux is mostly greater than the blue around the world. Expanding crops and irrigation to feed a growing human population will shift more blue water into green, exacerbating the blue water vulnerability to future climate change. These results are important for guiding land-use planning to optimally balance various freshwater needs on land. Water on land is partitioned to a green flux that mainly sustains terrestrial ecosystems and societal food security, and a blue flux that mainly sustains aquatic ecosystems and societal water security. Data and a global machine learning model show greater green than blue flux pa